With the development of the lighting technology, a wide variety of light sources become available. These light sources may be TL lamps, halogen lamps, light-emitting diodes (LEDs) and other light sources.
Also, people's requirements on lighting become higher and higher. An intensity or a color variation of light emitted by a light source may be adjusted by manually turning on a mechanical switch. However, the way of adjustment by mechanical switches may not only require a manual operation but also may have poor adjustability and cannot obtain an optimum illuminating effect.